Transmission brakes are used in shiftable transmissions, especially in those of commercial vehicles, in order to brake their countershafts so that shifting is faster and without double clutches. In vehicles with a clutch between the engine and the transmission, the actuation of the transmission brake can be effected in conjunction with the actuation (or disengaging) of a clutch. In doing so, a transmission brake cylinder is supplied with compressed air to make the transmission brake act.
The transmission brake is actuated automatically in automated manual transmissions. Automated actuation using compressed air and via corresponding shifting elements is effected for this purpose. Instead of pneumatic actuation, provision can also be made for hydraulic actuation. A piston is slidably held in the transmission brake cylinder and is reset, particularly by spring action, as soon as the fluid can escape from the transmission brake cylinder.
DE 10 2013 016 759 A1 discloses an assembly for actuating a transmission brake cylinder, particularly in conjunction with automated manual transmissions of commercial vehicles or buses, in which a transmission brake cylinder can be supplied with fluid from a brake line and in which a piston in the transmission brake cylinder can be reset by spring action. The assembly comprises two control valves, which can be used to control the pressure in the transmission brake cylinder and of which at least one is a power operated control valve. The two valves are arranged and configured such that fluid can escape from the transmission brake cylinder in the absence of power to the control valve. A disadvantage of this assembly lies in the fact that it only has weak exhausting dynamics. As a result the transmission brake cylinder cannot be exhausted fast enough in time-sensitive shifting situations.